1. Field of the Invention
This invention relates to a thermoplastic resin composition and a temperature-dependent shape-transformable/fixable (i.e., shape-transformable and shape-fixable) product (e.g., molded product) making use of the same. More particularly, it relates to a thermoplastic resin composition prepared by melt-blending a thermoplastic resin and a thermoplastic polymer having a glass transition temperature within a specific temperature range, being transformable to any desired shapes upon application of an external stress in a suitable temperature region higher than a temperature about the glass transition temperature, and having the function to become fixed to the transformed shape in a temperature region lower than the glass transition temperature; and a temperature-dependent shape-transformable/fixable product obtained using such a composition.
2. Description of the Related Art
Shape memory resins comprised of a single resin such as polynorbornene polymer or styrene-butadiene copolymer and shape memory resins comprised of a composite resin obtained by blending trans-form polyisoprene resin with polyolefin resin are known in the art.
Some proposals are also disclosed with regard to temperature-dependent shape-transformable resin compositions that are caused to transform in a temperature range higher than glass transition temperature and become fixed to the transformed shape upon cooling. For example, U.S. Pat. No. 4,891,409 discloses a single-phase shape-transformable elastomer compound comprised of a crystalline polymer and an elastomer polymer which are homogeneously mutually melted, having a single and overall glass transition temperature.
Now, those comprised of polynorbornene polymer are high-molecular compounds having about millions of molecular weight, and have a difficulty in moldability for injection molding or the like, having limitations on their use. Moreover, they have shape memory temperatures specific to such polymers, and can not be set at a variety of temperatures adapted to purposes.
Those of the styrene-butadiene copolymer type have limitations on their use because of a relatively high shape memory temperature (about 60-90.degree. C.) and poor thermal properties.
Those of the combination type comprised of polyolefin resin and trans-form polyisoprene resin are those which are caused to transform at a temperature higher than the melting point of the polyisoprene resin to bring out shape memory performance, thus they are necessarily shape-transformable only in a high temperature region.
The one disclosed in U.S. Pat. No. 4,891,409 is a single-phase temperature-dependent shape-transformable resin composition obtained by mutually melting a crystalline polymer and an elastomer polymer. When this composition is made into molded products and the molded products are left to stand in contact, they may stick together to become separable with difficulty. This is not preferable for their handling or storage at the stage of manufacture. Also, the proportion of crystallization and the degree of cross-linking, i.e., the formation of a three-dimensional network affects the relative readiness in shape transformation and the degree of its restoration, and delicate control therefor must be taken into account. Thus, not only the freedom of function setting is restricted but also difficulties may arise such that the function of elongation and elastic restoration is prohibited by the cross-linking.